IMD lowers monsoon forecast, raises spectre of drought
The India Meteorological Department (IMD) revised its Southwest Monsoon (SWM) forecast for 2026 downward to 90% of the Long Period Average (LPA), the thresho...
What Happened
- The India Meteorological Department (IMD) revised its Southwest Monsoon (SWM) forecast for 2026 downward to 90% of the Long Period Average (LPA), the threshold at which a season is classified as "deficient."
- IMD placed the probability of a deficient monsoon season at 60%, with an additional 24% chance of below-normal rainfall — meaning a combined 84% probability of below-normal or deficient conditions.
- Only parts of the Northeast and isolated pockets of Northwest India are forecast to receive normal to above-normal rainfall; most of the country, including Central, South Peninsular, and Northwest India, faces moisture deficits.
- The forecast is linked to a 92% probability of El Niño conditions developing in the equatorial Pacific Ocean during the June–September monsoon window.
- Official data pegs the LPA (1971–2020 reference period) at approximately 868.6 mm of rainfall for the country as a whole.
Static Topic Bridges
Long Period Average (LPA) and IMD Rainfall Categories
The Long Period Average is the mean rainfall recorded over a defined region and season, averaged over a 50-year reference period. IMD currently uses 1971–2020 as the reference, which yields an all-India seasonal average of approximately 868.6 mm. LPA serves as the benchmark against which current-year performance is measured.
- Normal / Near-Normal: 96–104% of LPA (departure within ±10%)
- Below Normal: 90–96% of LPA
- Deficient: less than 90% of LPA
- Above Normal: 104–110% of LPA
- Excess: more than 110% of LPA
- IMD issues seasonal outlooks in two stages — a preliminary April forecast and a revised May forecast — both using ensemble modelling from more than 2,400 observation stations and 3,500 rain-gauge stations.
Connection to this news: At 90% of LPA, the 2026 forecast sits exactly on the boundary between "below normal" and "deficient," and the 60% probability weight assigned to the deficient category signals a historically significant drought risk.
Southwest Monsoon — Mechanism and Agriculture Linkage
The Southwest Monsoon (June–September) accounts for roughly 75% of India's annual rainfall and irrigates nearly half of the net sown area. It is driven by the differential heating of the Asian landmass relative to the Indian Ocean, which creates a low-pressure system over the subcontinent drawing in moisture-laden winds from the Arabian Sea and the Bay of Bengal.
- Normal onset at Kerala: June 1 (±7 days by historical average)
- Two branches: Arabian Sea branch (west coast, Deccan, central India) and Bay of Bengal branch (northeast, Gangetic plain)
- A deficient monsoon historically correlates with lower Kharif crop yields (paddy, pulses, oilseeds), reduced reservoir storage, and subsequent water stress in Rabi season.
- India receives about 4,000 billion cubic metres of precipitation annually; SWM contributes the dominant share.
Connection to this news: A deficient SWM in 2026 would directly threaten Kharif sowing targets and could trigger food-price inflation — both themes tested in UPSC GS Paper 3.
El Niño and Its Suppressive Effect on Indian Monsoon
El Niño refers to the anomalous warming of sea surface temperatures (SSTs) in the central and eastern equatorial Pacific Ocean, occurring as part of the El Niño–Southern Oscillation (ENSO) cycle. During El Niño, the Walker Circulation — the east-west overturning of air over the tropical Pacific — weakens, suppressing convection over the Indian Ocean and reducing moisture inflow into the subcontinent.
- El Niño events recur every 2–7 years on average and typically last 9–12 months.
- Historically, about 60–70% of strong El Niño years correspond to below-normal or deficient Indian monsoons.
- Notable drought years associated with El Niño: 1987, 2002, 2009, 2014–15.
- The Indian Ocean Dipole (IOD) can moderate El Niño's impact: a positive IOD counteracts suppression; a negative IOD compounds it.
Connection to this news: With a 92% probability of El Niño development during the 2026 SWM season, IMD's revised downward forecast is mechanistically consistent with the historical El Niño–drought link.
Key Facts & Data
- 2026 IMD forecast: 90% of LPA (revised downward from an earlier estimate)
- LPA reference period: 1971–2020; all-India seasonal average ≈ 868.6 mm
- Probability of deficient monsoon: 60%; combined below-normal or deficient probability: 84%
- Probability of El Niño development during SWM 2026: 92%
- Deficient threshold: below 90% of LPA
- Only Northeast and isolated Northwest pockets forecast to receive normal rainfall
- Monsoon accounts for ~75% of India's annual rainfall